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| 3. |
- Ceberg, S., et al.
(författare)
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FLASH radiotherapy and the associated dosimetric challenges
- 2023
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Ingår i: Journal of Physics: Conference Series. ; 2630
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Konferensbidrag (refereegranskat)abstract
- At Lund University and Skåne University Hospital in Lund, Sweden, we have, as the first clinic, modified a clinical Elekta Precise linear accelerator for convertible delivery of ultrahigh dose rate (FLASH) irradiation. Whereas recently published reviews highlighted the need for standardised protocols for ultra-high dose rate beam dosimetry to be able to determine the true potential of FLASH irradiation, several dosimetry studies as well as in-vitro and in-vivo experiments have been carried out at our unit. Dosimetric procedures for verification of accurate dose delivery of FLASH irradiation to cell cultures, zebrafish embryos and small animals have been established using radiochromic films and thermo-luminescent dosimeters. Also, recently the first experience of electron FLASH radiotherapy (FLASH-RT) in canine patients in our clinical setting was published. Our research facilities also include a laboratory for 3D polymer gel manufacturing. Recently, we started investigating the feasibility of a NIPAM polymer gel dosimeter for ultra-high dose rate dosimetry. Furthermore, in the bunker of the modified Elekta linear accelerator, a Surface Guided Radiotherapy (SGRT) system is accessible. The CatalystTM system (C-Rad Positioning, Uppsala, Sweden) provides optical surface imaging for patient setup, real-time motion monitoring and breathing adapted treatment. Aiming at treating patients using ultra-high dose rates, a real-time validation of the alignment between the beam and the target is crucial as the dose is delivered in a fraction of a second. Our research group has during the last decade investigated and developed SGRT workflows which improved patient setup and breathing adapted treatment for several cancer patient groups. Recently, we also started investigating the feasibility of a real-time motion monitoring system for surface guided FLASH-RT. Both FLASH related studies; 3D polymer gel dosimetry and surface guided FLASH-RT are to our knowledge the first of their kind. Following an introduction to the field of FLASH and the associated dosimetric challenges, we here aim to present the two ongoing studies including some preliminary results.
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| 4. |
- Konradsson, E., et al.
(författare)
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Development of dosimetric procedures for experimental ultra-high dose rate irradiation at a clinical linear accelerator
- 2022. - 1
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 2167
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Konferensbidrag (refereegranskat)abstract
- As radiotherapy using ultra-high dose rates has gained new interest, the dosimetric challenges arising at these conditions needs to be addressed. Ionization chambers suffer from a large decrease in ion collection efficiency due to ion recombination, making on-line dosimetry difficult. In this work we present experimental setups and dosimetric procedures for FLASH irradiation of cells, zebrafish embryos and small animals using a 10 MeV electron beam at a modified clinical linear accelerator, and describe the dosimetric steps required to initiate clinical trials. The dosimetric equipment used for our pre-clinical experiments consisted of radiochromic film, thermoluminescent dosimeters, a Farmer-type ionization chamber and phantom material mimicking the experimental setup for irradiation. In preparation for small animal irradiation, dose profiles and depth dose curves were measured for all collimator sizes. The average dose rates were ≥620 Gy/s, ≥640 Gy/s and ≥400 Gy/s for cells, zebrafish embryos and small animals, respectively.
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| 5. |
- Konradsson, E., et al.
(författare)
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Polymer gel dosimetry for experimental verification of conformal small animal irradiation at a preclinical research platform
- 2023
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Ingår i: Journal of Physics: Conference Series. - 1742-6596. ; 2630:1
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Tidskriftsartikel (refereegranskat)abstract
- In translational research, there is a need for preclinical studies of high quality that corresponds to the conformal dose distributions conventionally delivered to humans in the modern radiotherapy clinic. To facilitate this need, novel preclinical systems consist of preclinical radiation platforms and small animal treatment planning systems. However, small-field dosimetry is challenging and requires dosimeters with high spatial resolution. In this study we demonstrate the feasibility of experimentally validating the dose distribution in small fields at a preclinical X-ray research platform using a polymer gel dosimeter and MRI-readout.
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| 6. |
- Bäck, S. Å.J., et al.
(författare)
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4D dosimetry and motion management in clinical radiotherapy
- 2019. - 1
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1305
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Konferensbidrag (refereegranskat)abstract
- Many novel modulated radiation treatment techniques are sensitive to patient motion which may degrade the dose distribution considerably. As there may be a simultaneous movement of the tumour and treatment machine, undesired heterogeneities in the dose distribution can be resulted. Methods to estimate the dosimetric effect of motion and treatment deliveries for both photons and protons are needed. We have recently studied Hodgkin's lymphoma, liver and left sided breast cancer cases and developed tools to be able to simulate simultaneous organ movement and treatment delivery. Furthermore, it is of great importance to validate potential simulations in a realistic quality control set-up, ideally including a complete dosimetry volume and movement/deformation (4D). Radiation sensitive deformable gels have the potential to meet this dosimetry challenge owing to the unique 3D characteristic to form both phantom and detector in one volume. Multi-array detectors together with a moving platform and a realistic object trajectory is an alternative to evaluate the clinical setting. The evaluation could then in principle be done on-line. Gel/plastic 3D dosimeters have the potential to also be irradiated during motion in a similar matter but have to be read-out post irradiation.
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| 7. |
- Edvardsson, A., et al.
(författare)
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Breathing-motion induced interplay effects for stereotactic body radiotherapy of liver tumours using flattening-filter free volumetric modulated arc therapy
- 2019
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 64:2
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study was to investigate breathing-motion induced interplay effects for stereotactic body radiotherapy (SBRT) of liver tumours treated with flattening-filter free (FFF) volumetric modulated arc therapy (VMAT). Ten patients previously treated with liver SBRT were included in this study. All patients had four-dimensional computed tomography (4DCT) scans acquired prior to treatment. The 4DCT was sorted into 8-10 phases covering an equal time interval. A FFF VMAT plan was created for one fraction in the mid-ventilation phase for each patient. To generate dose distributions including both interplay effects and dose blurring, a sub-plan was calculated for each phase. The total dose distributions were accumulated to the mid-ventilation phase using the deformed vector fields (DVF) from deformable image registration between the corresponding CT and the mid-ventilation phase CT. A blurred dose distribution, not including interplay effects, was also obtained by distributing the delivery of the whole plan uniformly on all phases, and was similarly accumulated to the mid-ventilation phase. To isolate interplay effects, this blurred dose distribution was subtracted from the total dose distribution with interplay effects. The near minimum dose (D-98%), mean dose (D-mean), heterogeneity index (HI), and the near minimum dose difference (Delta D-98%) between the accumulated dose distributions with and without interplay effects were calculated within the gross tumour volume (GTV) for each patient. Comparing the accumulated dose distributions with and without interplay effects, the D-98(%) decreased for nine of the ten patients and the HI increased for all patients. The median and minimum differences in D-98(%) were -2.1% and -5.0% (p = 0.006), respectively, and the median HI significantly increased from 6.2% to 12.2% (p = 0.002). The median Delta D-98% was -4.0% (range - 7% to - 1.5%). In conclusion, statistically significant breathing-induced interplay effects were observed for a single fraction of FFF VMAT liver SBRT, resulting in heterogeneous dose distributions within the GTV.
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| 8. |
- Johansson, Edvin, et al.
(författare)
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Perfusion assessment with bolus differentiation : a technique applicable to hyperpolarized tracers
- 2004
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Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 52:5, s. 51-1043
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Tidskriftsartikel (refereegranskat)abstract
- A new technique for assessing tissue blood flow using hyperpolarized tracers, based on the fact that the magnetization of a hyperpolarized substance can be destroyed permanently, is described. Assessments of blood flow with this technique are inherently insensitive to arterial delay and dispersion, and allow for quantification of the transit time and dispersion in the arteries that supply the investigated tissue. Renal cortical blood flow was studied in six rabbits using a 13C-labeled compound (2-hydroxyethylacrylate) that was polarized by the parahydrogen-induced polarization (PHIP) technique. The renal cortical blood flow was estimated to be 5.7/5.4 +/- 1.6/1.3 ml/min per milliliter of tissue (mean +/- SD, right/left kidney), and the mean transit time and dispersion in the renal arteries were determined to be 1.47/1.42 +/- 0.07/0.07 s and 1.78/1.93 +/- 0.40/0.42 s2, respectively.
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| 9. |
- Svensson, H., et al.
(författare)
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Feasibility study using MRI and two optical CT scanners for readout of polymer gel and Presage (TM)
- 2013
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Ingår i: 7th International Conference on 3D Radiation Dosimetry (IC3DDose). - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 444, s. 012079-012079
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Konferensbidrag (refereegranskat)abstract
- The aim of this study was to compare the conventional combination of three-dimensional dosimeter (nPAG gel) and readout method (MRI) with other combinations of three-dimensional dosimeters (nPAG gel/Presage (TM)) and readout methods (optical CT scanners). In the first experiment, the dose readout of a gel irradiated with a four field-box technique was performed with both an Octopus IQ scanner and MRI. It was seen that the MRI readout agreed slightly better to the TPS. In another experiment, a gel and a Presage (TM) sample were irradiated with a VMAT field and read out using MRI and a fast laser scanner, respectively. A comparison between the TPS and the volumes revealed that the MRI/gel readout had closer resemblance to the TPS than the optical CT/Presage (TM) readout. There are clearly potential in the evaluated optical CT scanners, but more time has to be invested in the particular scanning scenario than was possible in this study.
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| 10. |
- Ceberg, Sofie, et al.
(författare)
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RapidArc treatment verification in 3D using polymer gel dosimetry and Monte Carlo simulation.
- 2010
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 55:17, s. 4885-4898
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to verify the advanced inhomogeneous dose distribution produced by a volumetric arc therapy technique (RapidArc) using 3D gel measurements and Monte Carlo (MC) simulations. The TPS (treatment planning system)-calculated dose distribution was compared with gel measurements and MC simulations, thus investigating any discrepancy between the planned dose delivery and the actual delivery. Additionally, the reproducibility of the delivery was investigated using repeated gel measurements. A prostate treatment plan was delivered to a 1.3 liter nPAG gel phantom using one single arc rotation and a target dose of 3.3 Gy. Magnetic resonance imaging of the gel was carried out using a 1.5 T scanner. The MC dose distributions were calculated using the VIMC-Arc code. The relative absorbed dose differences were calculated voxel-by-voxel, within the volume enclosed by the 90% isodose surface (VOI(90)), for the TPS versus gel and TPS versus MC. The differences between the verification methods, MC versus gel, and between two repeated gel measurements were investigated in the same way. For all volume comparisons, the mean value was within 1% and the standard deviation of the differences was within 2.5% (1SD). A 3D gamma analysis between the dose matrices were carried out using gamma criteria 3%/3 mm and 5%/5 mm (% dose difference and mm distance to agreement) within the volume enclosed by the 50% isodose surface (VOI(50)) and the 90% isodose surface (VOI(90)), respectively. All comparisons resulted in very high pass rates. More than 95% of the TPS points were within 3%/3 mm of both the gel measurement and MC simulation, both inside VOI(50) and VOI(90). Additionally, the repeated gel measurements showed excellent consistency, indicating reproducible delivery. Using MC simulations and gel measurements, this verification study successfully demonstrated that the RapidArc plan was both accurately calculated and delivered as planned.
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